1. Field of the Invention
The present invention relates to a light scanning technique of reflecting and deflecting incident light by a rotary deflector, and particularly a technique of reducing the influence of a thrust-direction force generated by air resistance received by a reflection surface of the rotary deflector.
2. Description of the Related Art
Traditionally, there has been known a technique of causing a luminous flux from a light source to scan the photoconductive surface of each of the plural photoconductors by using a rotary deflector and thus forming an image such as an electrostatic latent image on the photoconductors.
In the traditional technique, plural reflection surfaces of the rotary deflector which carries out scanning of the plural photoconductors with a light beam are tilted in the same direction with respect to the rotation axis (see, for example, JP-A-2000-2846).
In the traditional technique, since the plural reflection surfaces of the rotary deflector are tilted in the same direction with respect to the rotation axis, a deviated thrust-direction force directed toward one of the directions of rotation axis (thrust directions) is generated by the influence of air resistance when the rotary deflector rotates.
In such a traditional light scanning technique, the rotary deflector may be driven at plural patterns of rotation speeds in order to deal with different printing speeds, and the force applied in the axial direction is changed by the variance in the rotation speed. Such variance in the thrust-direction force causes change in the position in the axial direction of the rotary deflector and hence may cause variance in optical characteristics.
Also, in circumstances where the position in the direction of rotation axis of the rotary deflector changes in this manner, it is necessary to secure a broad effective reflection area in the axial direction of the rotary deflector (to increase size of the rotary deflector in the direction of rotation axis) in order to make a luminous flux incident in the effective reflection area on the reflection surfaces of the rotary deflector even when the change in the position has occurred.
Such expansion of the effective reflection range of the rotary deflector increases windage loss at the time when the rotary deflector rotates, and thus increases motor load and noise.
The change in the position in the direction of rotation axis of the rotary deflector as described above can be restrained if a bearing or the like that can deal with the thrust-direction force is employed. However, there is a problem that the device becomes expensive.